1. Field of the Invention
The present invention relates to an optical beam axis adjustment apparatus for automatedly adjusting a vertical angle of an optical beam of a head lamp for use in vehicle.
2. Brief Description of the Prior Art
A main body of a vehicle, in particular of an automobile car, is apt to incline upwardly and downwardly with respect to a horizontal plane in a back and forth direction, depending upon a number of riding passengers and a loading status of luggage. The term "main body of a vehicle" is defined herein as a "main body of a vehicle including a carrosserie and a chassis no matter what a formed status may be monocoque or separate". The term "back and forth direction" is simultaneously defined herein as a "direction similar to those toward which a ship, an airplane etc. incline their bodies when they are pitching". During the inclination, an orienting direction of a head lamp varies corresponding to an angle at which a bottom surface of the main body intersects the horizontal plane. As a result, it has so far been proposed to adjust vertically an optical beam axis of the head lamp corresponding to an inclining angle of the main body in the back and forth direction.
FIG. 5 is a side view showing a schematic constitution of such a sort of mechanisms as automatedly adjusting the optical beam axis of the head lamp. In FIG. 5, stroke sensors 1 and 2 are provided which are connected through a suspension arm and a link, respectively, to a front wheel and a rear wheel. An upward and downward movement of each wheel is transformed into each rotation angle of the stroke sensors 1 and 2. Output voltages produced corresponding to aforesaid rotation angles are applied to an electric control unit (referred to as "ECU") 3.
The control unit 3 calculates the inclination angle of the main body in the back and forth direction from applied input data for measuring the upward and downward movements of the front and the rear wheels as well as from a distance between two axles, namely a wheelbase. Herein the inclination angle .theta. of the main body is represented by a following equation: EQU .theta.tan-1(.DELTA.h/L) (1)
wherein .DELTA.h is a difference in height between the front wheel and the rear wheel while L is the distance between the two axles.
An electric signal produced from the ECU 3 moves either upwardly or downwardly the optical beam axis of the head lamp through an actuator 4 toward a reverse direction with respect to that the main body inclines as far as aforesaid difference in inclination angle .theta. from an initial position of the main body which is calculated by Equation (1) around a lamp supporting portion as a supporting point.
Because aforesaid adjustment in optical beam axis of the lamp is performed only to an extent of the weight variation in main body which is induced by changes in numbers of the passengers and the luggage, the adjustment is carried out with respect to the inclining angle of the main body during a standstill of the vehicle.
However, the conventional optical beam adjustment apparatuses mentioned above have some problems that the adequate optical beam axis adjustment cannot be performed, depending upon the various statuses of the vehicles and traffic roads.
For instance, when a judgment whether the vehicle is now traveling or stopping is passed by reading sensing pulses for sensing a car speed before computing the inclining angle of the main body during stopping, the sensing pulses for sensing the car speed are frequently delayed to be applying to an input terminal. If the main body changes in attitude during starting before the input pulses for sensing the car speed are applied, the optical beam axis adjustment cannot be performed when the car speed pulses are applied later even though the attitude of the main body has changed from the attitude during the standstill.
On the other hand, if the optical beam axis is subjected to the adjustment every time when the vehicle stops, the adequate lamp angle cannot be obtained because the optical beam axis varies due to road situations such as a slope of a road or waviness of the road surface even though there exists no variation in load of the vehicle.
If the car speed sensing pulses are not applied because a failure mode takes place, for instance, in the car speed sensor, the optical beam axis adjustment operates even during the traveling of the vehicle, which is inconvenient to the system on the contrary.
Furthermore, a positioning adjustment is necessary during equipping the stroke sensors for use in detecting the inclination angle of the main body because a precision in positioning for equipping the stroke sensors is required. However, the positioning adjustment during equipping the stroke sensors is too difficult to attain a suitable lamp angle.